Data recording disk drives, such as magnetic recording disk drives, store information in data tracks on the data surface of a rotatable magnetic recording disk. A read/write head or transducer that reads data from and writes data to the data surface is located on an air-bearing slider that is supported by a cushion of air on the rotating disk. The slider is attached to a flexible suspension at the end of a rigid arm and is moved generally radially from track to track by an actuator. The disk drive actuator is typically a rotary voice coil motor (VCM) that moves the actuator arm and the attached suspension and slider generally radially to position the head at the desired track under the control of a servo control system that receives pre-recorded servo position information from the data surface. As the data tracks on the disk are made narrower and placed closer together to increase the data density, it becomes increasingly difficult for the actuator and the servo control system to quickly and accurately position the head over the desired track and to provide track following. For example, a servo control system with a VCM actuator will have difficulty achieving a servo loop bandwidth greater than 2 kHz.
Electrostatic actuators have been proposed for attachment to the suspension to provide a secondary fine positioning of the head while the primary actuator provides the coarse positioning. One such secondary actuator is a rotary electrostatic microactuator (so called because it is a micro-electromechanical system (MEMS) device) described in IBM's U.S. Pat. Nos. 5,959,808 and 5,995,334, and in the paper by T. Hirano et al. “HDD TRACKING MICROACTUATOR AND ITS INTEGRATION ISSUES”, ASME International Mechanical Engineering Congress and Exposition, Orlando, Fla., pp. 449-452, November 2000. Advances in integrated circuit technology in recent years have led to the development of MEMS devices of micrometer dimensions that can be actuated and controlled using electrostatic and other methods, such as mechanical, electromagnetic, fluidic and thermal. MEMS manufacturing technologies are a combination of the more established semiconductor microfabrication techniques with newer developments in micromachining.
The slider, which supports the read/write head and is attached to the movable portion of the electrostatic microactuator, must always be at ground electrical potential (zero volts) to avoid electrostatic discharge (ESD) between the slider and disk, which would damage the read/write head. Because the microactuator's movable electrodes are electrically grounded, a relatively high voltage (as high as 60V) is needed to generate reasonable force. Also, because the slider ground and the microactuator ground are connected, there can be an electrical coupling between the microactuator driver signal and the magnetic signal from the read/write head, which adds undesirable noise to the magnetic signal.
What is needed is a disk drive electrostatic microactuator and driver circuitry that does not suffer from the disadvantages of microactuator grounding and relatively high voltages.